A particular classification of fast nuclear reactor, referred to as a “breed-and-burn” fast reactor, includes a nuclear reactor capable of generating more fissile nuclear fuel than it consumes. That is, the neutron economy is high enough to breed more fissile nuclear fuel (e.g., plutonium-239) from fertile nuclear reactor fuel (e.g., uranium-238) than it burns in a fission reaction. In principle, a breed-and-burn reactor may approach an energy extraction rate of 100% of the fertile materials. To initiate the breeding process, a breed-and-burn reactor must first be fed with an amount of fissile fuel, such as enriched uranium. Thereafter, breed-and-burn reactors may be able to sustain energy production over a timespan of decades without requiring refueling and without the attendant proliferation risks of conventional nuclear reactors.
One type of breed-and-burn reactor is a molten salt reactor (MSR). Molten salt reactors are a class of fast spectrum nuclear fission reactors wherein the fuel is a molten salt fluid containing mixed or dissolved nuclear fuel, such as uranium or other fissionable elements. In an MSR system, the unmoderated, fast neutron spectrum provided by fuel salts enables good breed performance using the uranium-plutonium fuel cycle. In contrast to the fast spectrum neutrons that dominate breeding of fissile fuel from fertile fuel, thermal neutrons dominate the fission reaction of fissile fuel. A fission reaction resulting from a collision of a thermal neutron with a nuclide can consume the fissile fuel in a fission reaction, releasing fast spectrum neutrons, gamma rays, large amounts of heat energy and expelling fission products, such as smaller nuclei elements. Consuming nuclear fuel is referred to as burnup or fuel utilization. Higher burnup typically reduces the amount of nuclear waste remaining after the nuclear fission reaction terminates. The fast neutron spectrum also mitigates fission product poisoning to provide exceptional performance without online reprocessing and the attendant proliferation risks. The design and operating parameters (e.g., compact design, low pressures, high temperatures, high power density) of a breed-and-burn MSR, therefore, offer the potential for a cost-effective, globally-scalable solution to zero carbon energy.